In 1989, Mizell established the label Jam Master Jay Records, which scored a strong success in 1993 with the band Onyx. He also connected Chuck D with Def Jam co-founder Rick Rubin. (Def Jam's other founder, Russell Simmons, is the brother of DJ Run.)
In the 1990s, Mizell survived a bad car accident and a gunshot wound.
On October 30, 2002, he was shot and killed in a Merrick Boulevard recording studio in Queens, New York. The other person in the room, twenty-three-year-old Urieco Rincon, was shot in the ankle and survived.
The New York Daily News reported that authorities have investigated whether Kenneth "Supreme" McGriff, a convicted drug dealer and longtime friend of Murder Inc. heads Irv Gotti and Chris Gotti, targeted Mizell because the DJ defied an industry blacklist of rapper 50 Cent that was imposed because of "Ghetto Qur'an", a song 50 Cent wrote about McGriff's drug history. A 2003 affidavit says: "Law enforcement agents are investigating the possibility that [Jason] Mizell was murdered for defying the blacklist of 50 Cent."
In April 2007, federal prosecutors named Ronald "Tenad" Washington as an accomplice in the murder of Mizell. Washington also is a suspect in the fatal shooting of Randy Walker in 1995, a close associate of the late rapper Tupac Shakur. For his part, Washington “pointed his gun at those present in the studio, ordered them to get on the ground and provided cover for his associate to shoot and kill Jason Mizell,” prosecutors said in court papers.
Mizell is survived by his wife Terri and three children. He is buried at the Ferncliff Cemetery in Hartsdale, New York. His favorite long brown leather trench coat was given to his best friends, Rev Run and DMC.